Tectonic evolution and depositional response in southern continental marginal basins of South China Sea during period of rift-drift-foreland: A case study from the Liyue Basin

Abstract

Based on the analysis of tectonics-stratigraphy-sedimentology in Liyue Basin, this paper finds out the characteristics of tectonic evolution and sedimentary fillings, reveals the genetic relationship between the basin evolution and the spreading of the South China Sea (SCS), and provides the reference for the study on the marginal sea evolution of the SCS.The Cenozoic tectonic-sedimentary evolution of the Liyue Basin could be divided into three distinct stages: the first stage characterized by continental marginal rifting and littoral-neritic clastic sedimentation from Paleocene to Early Oligocene, the second stage characterized by detaching-drifting and neritic carbonate sedimentation from Late Oligocene to Early Miocene, and the third stage featured with peripheral foreland flexure subsidence and regional differential sedimentation since Middle Miocene.In the first stage from Paleocene to Early Oligocene, the southeastward subduction of the Proto-South China Sea (PSCS) resulted in the passive rifting of the ancient South China Plate under the action of horizontal extension, and then the formation of the Liyue Rifting Basin.During this period dominated by the littoral-neritic depositional environment from Paleocene to Early Oligocene, controlled by detrital sediments supply and the PSCS action, a series of relatively large-scale braided river deltas developed in the northwestern basin, however, few small-scale fan deltas developed on the edge of the isolated uplifts in the eastern and southern basin adjacent to the PSCS.In the second stage from Late Oligocene to Early Miocene, accompanying with the PSCS continuous subduciton and the SCS initialization and spreading, the Liyue Basin located on the Liyue-Balawan Plate detached from the South China ancient continent, and then southwards drifted with slow subsidence and weak faulting.During this period dominated by the neritic- bathyal depositional environment from Late Oligocene-Early Miocene, due to the scarcely detrital sediment supply, large-scale carbonate platforms and reefs developed in the northern basin, while the bathyal environment was generally founded in the south.In the third stage since Middle Miocene, the process that the SCS spreading had being ceased and the Liyue-Balawan block was subducting towards Philippine island arc, led to the beginning of the evolution of the foreland basin in the Liyue Basin, characterized by asymmetric flexure subsidence, increasing water depth, and enhanced fault activity.During this period dominated by the bathyal- neritic depositional environment, it is the predominant feature that the carbonate platforms and reefs and deepwater gravity flow deposits have respectively being developed in the north and partial south of the Liyue Basin.It could be concluded that the tectonic-sedimentary evolution in Liyue Basin was closely related to the subduction-extinction of the PSCS and the spreading-closure of the SCS